The only reason Buu got that nose is because he absorbed Gotenks, Piccolo, and Gohan. After they were removed from Buu by Goku and Vegeta (they severed their pods that were inside Buu's body), Buu lost his human-like characteristics.

He was at the start, but Yamcha, Krillin, Chiaotzu and Tien all studied under King Kai making them much more powerful.
There could be something I'm missing though, I'm happy to be proven wrong as I love Roshi

It's due to excellent ki control and a better philosophical basis to his style than Tien. In the crane school, life is seen as expendable so it may be thrown away to ensure you win a fight. The turtle school teaches to stick things out until the end and to defend life.

The loss of Fat Buu's innocence made him more dangerous and probably stronger. But the loss of Gohan, Piccolo, and Gotenks definitely made him weaker. I'd say Kid Buu = Fat Buu but is much more aggressive and deadly.